The degree of integration of integrated circuits has increased more and more. Under these circumstances, it has become necessary to work ultrafine patterns comprising lines with a width of less than quarter micron in the art of production of semiconductor substrates for super LSI, etc. As a means for providing a finer pattern there is known a method involving the use of an exposing light source having a shorter wavelength for the formation of resist pattern.
For the production of semiconductor elements having an integration degree of up to 64 M bits, i-ray (365 nm) emitted by a high voltage mercury vapor lamp has been used to date. As positive-working resists adapted for this light source there have been developed many compositions containing a novolac resin and a naphthoquinonediazide compound as a photosensitive material. These compositions have produced sufficient results in the work of lines having a width of about 0.3 μm or greater. For the production of semiconductor elements having an integration degree of 256 M bits or greater, KrF excima laser beam (248 nm) has been employed as an exposing light source instead of i-ray.
For the purpose of producing semiconductor elements having an integration degree of 1 G bits or greater, the use of ArF excima laser beam (193 nm), which has a shorter wavelength, has been studied. Further, the use of F2 excima laser beam (157 nm) has been studied for the formation of patterns having a line width of not greater than 0.1 μm.
In order to cope with the reduction of the wavelength of these light sources, the constituents of resist material and the compound structure thereof have been changed drastically.
As a resist composition adapted for exposure to KrF excima laser beam there has been developed a so-called chemically-sensitized resist, i.e., composition comprising in combination a resin protected by an acid-decomposable group having a basic skeleton made of a poly(hydroxystyrene) having a small absorption at 248 nm as a main component and a compound which produces an acid when irradiated with far ultraviolet ray (photo-acid generator).
As a resin composition adapted for exposure to ArF excima laser beam (193 nm) there has been developed a chemically-sensitized resist comprising an acid-decomposable resin having an alicyclic structure having no absorption at 193 nm incorporated therein in its polymer main chain or side chain.
Referring to F2 excima laser beam (157 nm), it was found that even the aforementioned alicyclic resin shows a great absorption at 157 nm and thus leaves something to be desired in the formation of desired patterns having a line width of not greater than 0.1 μm. It is reported in Proc. SPIE. Vol. 3678. page 13 (1999) that a resin having fluorine atom (perfluoro structure) incorporated therein has a sufficient transparency to F2 excima laser beam (157 nm). The structure of effective fluororesins are proposed in Proc. SPIE. Vol. 3999. page 330 (2000), page 357 (2000), page 365 (2000), WO-00/17712, etc. Thus, resist compositions containing fluororesin have been studied.
However, these resist compositions leave something to be desired in various properties such as transparency, sensitivity and resolving power. These fluororesins also are disadvantageous in that they have a poor coatability.
Moreover, resist compositions containing fluororesin adapted for exposure to F2 excima laser beam have problems with line edge roughness, defective development and development residue (scum). It has been thus desired to solve these problems.
The term “line edge roughness” as used herein is meant to indicate that the edge on the border of the line pattern on the resist with the substrate has a shape having an irregular change in the direction perpendicular to the line direction. When this pattern is observed from above, the edge shows unevenness (± few nanometers to scores of nanometers). This roughness can be transferred to the substrate at the etching step. Thus, when this roughness is great, electrical defectives occur, resulting in the drop of yield.